The dangers of driving after too much coffee

Tired motorists relying on caffeine to keep them alert tip the balance into the caffeine danger zone and could be putting themselves and others at risk. Photo / 123rf

Coffee has long been a go-to for tired drivers. A quick shot of bean juice from a cafe or the gas station acts as a livener on a long journey. And thanks to our national habit of drinking one or two cups of coffee a day, we are consuming more caffeine than ever.

The growing popularity of stronger coffee beverages and caffeinated energy and sports drinks has also lead to a rise in caffeine consumption.

Caffeine is a stimulant. It blocks the effects of the neurotransmitter adenosine, which makes you feel tired, relaxed and sleepy.

According to Healthify / He Puna Waiora, the recommended maximum daily caffeine intake in Aotearoa New Zealand is no more than 400mg per day from all food and drink sources. If you’re pregnant or breastfeeding, it’s recommended you should have less than 200mg per day.

A typical cup of instant coffee contains 30-90mg, while a single shot of espresso in a barista coffee typically contains 100mg. However, most coffee chains use multiple shots in different drinks. A flat white, for example, may contain 240mg of caffeine. Factor in an energy drink or two, and it’s easy to get over-caffeinated. One 330ml can of Prime Energy contains 140mg of caffeine, while a 250ml can of Red Bull contains 80mg of caffeine.

Suddenly, lorry drivers, Uber drivers and tired motorists relying on caffeine to keep them alert tip the balance into the caffeine danger zone and could be putting themselves and others at risk. Using coffee when tired has been shown in studies to reduce accidents, but road safety experts are warning now that the effects of too much caffeine can also be dangerous.

A 2020 study by Loughborough University in the UK found that lorry drivers who had consumed large amounts of coffee and energy drinks reported having crashed more compared with those who had drunk only small quantities of caffeine. The high-use group also had poorer general health.

More recently, a survey conducted by vehicle financing company Carmoola found that one in four respondents also admitted that caffeine had left them feeling jittery, anxious or distracted when driving.

The company has launched a “curbing the caffeine” campaign to raise awareness of the dangers of driving after too much caffeine.

As part of the campaign, Dr Tim Mercer, a GP with Britain’s National Health Service, says: “Too much caffeine exaggerates some cardiovascular and urinary functions. It can cause pounding in the chest, tremors, jitteriness, anxiety, and it can affect mental health.”

So while drinking a few cups of tea or coffee during the day is fine, problems can arise for drivers who rely on coffee chains.

“These places often pack drinks full of espresso shots. One venti coffee from a well-known brand can push you very close to the limit. We’re petitioning for moderation rather than abstinence,” adds Dr Mercer, who drinks decaffeinated coffee.

With more people consuming more caffeine, the risks are increasing.

How too much coffee can impact your driving

1. Poor decision-making

James Gibson, the executive director of Road Safety GB, explains: “Neurological symptoms such as anxiety, dizziness and headaches can lead to poor decision-making and reduced concentration. Drivers are making decisions on a second-by-second basis, for example, deciding if it is safe to exit a junction or to change lanes. Poor decision-making can have significant safety implications for drivers, their passengers and other road users.

2. Tremors

Caffeine can overstimulate the central nervous system, resulting in hand or leg tremors, which make it harder to perform smooth, precise movements such as steering, gear-changing, or maintaining steady pressure on pedals. Shaking can translate into jerky steering inputs or overcorrections.

3. Slowed reactions

While moderate caffeine use improves alertness, excessive doses can tip you into jitters, anxiety and over-arousal, leading to delayed reaction times because of over-excited neural activity. It can also cause poor judgment of distance or speed.

4. Visual disturbances

High caffeine levels can cause eye muscle twitching and difficulty focusing, particularly when combined with fatigue or dehydration. These symptoms can cause blurred vision, rapid blinking, or increased distraction.

5. Headaches

Caffeine makes blood vessels in your brain constrict. That’s one reason it can relieve some headaches and is used in painkillers. But if you regularly consume a lot of caffeine, your body adapts by keeping those vessels slightly tighter than normal. Then, when caffeine levels drop, the vessels widen, causing a withdrawal headache.

Caffeine consumption and safe driving

Gibson advises: “Understand caffeine intake and consider if you are consuming more than the recommended safe daily limit of around 400mg. Drivers can moderate caffeine intake and ensure they are getting sufficient sleep and undertake habits for a good night’s sleep. Some slight changes can make a big difference to ensure positive sleep patterns, such as leaving sufficient time between your last caffeinated drink and bedtime. Drivers should not rely on caffeine to fight off tiredness – there is no substitute for good sleep.”

Does drinking caffeine sober you up?

No. Caffeine can mask the depressant effects of alcohol, but it can’t remove alcohol from your system. Debbie Shawcross, a professor of hepatology and chronic liver failure at the Institute of Liver Studies, King’s College London, explains: “The liver metabolises alcohol at a very constant rate, approximately one drink per hour. If there is excessive alcohol in the blood, the liver cannot speed up the detoxification process. There are no ways to speed up alcohol metabolism and no ways to avoid a hangover.”

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